This invention relates to balloon angioplasty, and particularly to angioplasty catheter systems utilizing multiple balloons and to angioplasty procedures utilizing those catheters.
Coronary angioplasty has emerged as the only viable present alternative to bypass surgery for revascularization of stenotic and occluded coronary arteries. Although transluminal angioplasty has application in peripheral artery disease, it is most widely used in the treatment of coronary artery disease. Unlike bypass surgery, percutaneous angioplasty does not require general anesthesia, cutting of the chest wall, extracorporeal perfusion or transfusion of blood. Percutaneous coronary angioplasty is not only less invasive and less traumatic to the patient, it is also less expensive because the angioplasty patient will have a shorter hospital stay and shorter post-procedure recovery time. Percutaneous transluminal angioplasty is performed by making a skin puncture with a specially-designed needle in one of the groins, and then introducing a guiding catheter (typically 8 or 9 French size) into the aorta and coronary artery orifice. A smaller caliber catheter which has a built-in inflatable and deflatable balloon of predetermined size and diameter is passed through the guiding catheter which is positioned in the opening of a target artery. This balloon catheter (with the balloon totally deflated by negative pressure) is advanced inside the target artery toward the point of obstruction that needs to be dilated. With the balloon portion of the catheter properly positioned inside the obstructed segment of the artery, under X-ray fluoroscopic observation, the balloon is inflatable by injecting contrast media mixed with saline at a pressure sufficient to overcome the resistance of the antherosclerotic plaque of the obstructed segment.
During the guiding catheter manipulation and especially while the balloon catheter is being advanced into the narrowed segment of the artery, X-ray fluoroscopy is used extensively. However, because one cannot ordinarily see the anatomy of an artery under X-ray fluoroscopy, contrast material is used. When contrast media is injected into an artery, details of the arterial anatomy are briefly visible until the contrast material flows away with the blood flow through the artery. Radiographic arteriograms are recorded during that brief moment of visualization. If the anatomic structures are complex and negotiating a particular arterial channel with the balloon catheter is difficult, frequent contrast injections during the procedure are necessary. However, there are limits to the amount of contrast material one can use in a given patient. For instance, the upper limit of Renografin-76 in a normal individual is approximately 3 c.c.'s per kilogram of body weight. The tolerance of a physically-ill individual may be substantially less. Excessive amounts of contrast material can be toxic to the kidneys, liver, and brain.
By inflating the balloon multiple times over a period of between 20-30 seconds and one or two minutes (allowing blood flow between inflations), the desired dilation of the obstructed segment of the artery can be achieved. When the desired results have been obtained by balloon inflations, the guiding catheter and the balloon catheter (with the balloon completely deflated with negative pressure) are withdrawn from the artery and the procedure is successfully terminated.
Atherosclerotic coronary artery disease is not curable. Both bypass surgery and balloon angioplasty are considered palliative treatments. Recurrence of disease after bypass surgery or coronary angioplasty is prevalent, and repeat procedures are not uncommon due to the nature of the disease. A patient may initially develop single-vessel coronary artery disease and then slowly progress into multiple-vessel disease over the years. Medication, bypass surgery or angioplasty do help to relieve the symptoms, but they generally cannot prevent a gradual progression of the disease.
Because the cost of bypass surgery is 2 to 2.5 times the cost of angioplasty, and because bypass surgery is more invasive, more traumatic, requiring longer hospital stays and longer post-operative recuperation, future demand for angioplasty is expected to grow as the physician skills and equipment technology expands. It has been estimated that the number of coronary artery angioplasties performed in the United States will double or triple to 450,000 or 500,000 cases per year by the early to mid 1990's. It also has been estimated that the number of multiple-vessel angioplasty cases will be from 2 to 2.5 times the number of single-vessel angioplasty cases. This will be a dramatic change from the situation in 1986 in which 70 to 80 percent of the coronary angioplasty cases are single-vessel dilations. The expected future growth of multi-vessel coronary angioplasty has serious technical and patient care implications. Present-day coronary angioplasty technology is based on the original single balloon concept which was designed to tackle single-vessel disease and thus single-vessel dilations. However, the single balloon technology is inadequate to meet the requirements of most multi-vessel disease situations.
During a typical coronary angioplasty, most of the procedure time is spent in certain preliminary steps that are necessary before the balloon can be inflated inside the obstructed segment of a target artery. In fact, the real job of dilating a vessel takes less than 20 percent of the total procedure time. The preliminary steps include patient (aseptic) preparation, groin preparation and needle puncture, insertion of the guidewire into the artery to introduce the guiding catheter, arterial heparinization, manipulation of the guiding catheter to cannulate the target coronary orifice, preliminary arteriography using contrast media injection into the artery and taking radiographic cine. Moreover, the balloon catheter must be prepared before it can be introduced into the target artery through the lumen of the guiding catheter. Preparation of the balloon catheter takes a minimum of 15-20 minutes. X-ray fluoroscopy and contrast media are extensively used during the guiding catheter and balloon catheter manipulations, especially when the balloon tip is being manipulated through the inside of the artery toward an obstructed segment which needs to be reopened by the balloon tip. Sometimes, the majority of the procedure time and the limits of the total allowable contrast volume are used up at this phase of a procedure. It is clear from the medical literature that the longer the procedure, the greater the risk of complications during cardiac catheterization. Likewise, the larger the volume of contrast material, the greater the chance of kidney failure or tissue toxicity, including brain and/or liver damage.
The size and diameter of the balloon to be used in a transluminal angioplasty should be approximately matched to the size and native diameter of the obstructed segment of the artery to be dilated. If the balloon size and diameter is smaller than the native artery, the results of balloon angioplasty are suboptimal, requiring a second dilation with a larger-sized balloon. In some cases, the result is a failed procedure, which may require either a second separate angioplasty procedure (especially if too much contrast material was already used) or bypass surgery. If the balloon is oversized in relation to the obstructed segment of the native vessel, the inner wall of the artery may dissect from the remainder of the artery and may occlude the vessel completely, causing total cessation of blood flow to the target area of the myocardium. This complication, except in rare occasions, leads to acute myocardial infarction and necessitates emergency bypass surgery. If the acute occlusion leads to a large infarction, death is a possibility.
The most common balloon diameters in demand for coronary angioplasties are 2.0 mm, 2.5 mm, 3.0 mm and 3.5 mm. The 2.0 mm and 2.5 mm balloons are used in patients with small caliber coronary arteries or in the distal coronary branches of patients with otherwise normal-sized coronary arteries. The 3.0 mm and 3.5 mm balloons are generally used in the proximal and larger native coronary arteries. If a patient has a single obstruction in the right or left coronary artery system, a single balloon cathether with a matching diameter and size will be selected for the intended dilation procedure. When the balloon is inflated inside the obstructed segment of the native artery, the balloon should maintain the original preshaped configuration and diameter under the maximum allowed pressure, which is generally up to 150 psi. Polymers such as PVC (polyvinylchloride) and various derivatives of polyethylene have proved to be suitable for making balloon catheters for coronary angioplasty. New polymer derivatives, including variations of Mylar material, are gaining popularity because of their high tensile strength and their potential for making very thin-walled dilation balloons.
In single lesion dilations, the choice of a properly-sized balloon catheter is relatively simple, although there are instances in which the original selection of the balloon catheter is inadequate so that a second balloon catheter is necessary to complete the procedure successfully. However, in multi-vessel disease, balloon catheter selection becomes compounded and complex. For example, a patient may have three lesions in his left coronary artery, and all three lesions may be approachable individually for successful balloon angioplasty. But such lesions may be in vessels of different sizes such as a 3.0 mm lesion in the proximal portion of the left anterior descending artery (LAD), a 2.0 mm lesion in the distal segment of the LAD, and a 2.5 mm lesion in the superior obtuse marginal artery. With currently available balloon catheters, angioplasty of these three differently-sized lesions is not always impossible, but it is cumbersome and inefficient. For each lesion, a matching balloon catheter is exchanged and manipulated into the target lesion under fluoroscopy with numerous contrast injections. To do this three times in a row requires roughly three times the procedure time, three times the contrast amount, and a minimum of three separate balloon catheters and their accessory devices. In light of the forecast that approximately two thirds of 450,000 to 500,000 patients in the 1990's will need multi-vessel coronary angioplasty, it is clear that there is a need for a major advance in balloon angioplasty that will provide more efficient and cost effective angioplasty balloon systems specifically designed (and suited) for multi-vessel coronary angioplasty.